1. Field of the Invention
The present invention relates to a channel divider to be used for reproducing a sound signal through a multiway speaker system and a method for setting its crossover frequency. The invention particularly relates to the channel divider that can suitably set the crossover frequency of the channel divider and can satisfactorily reproduce a sound when a biwiring-connectable speaker system including network circuits are used.
2. Description of the Related Art
In multiway speaker systems including woofers for low-pitched reproduction and tweeters for high-pitched reproduction, network circuits for dividing a band of a sound signal amplified by an amplifier according to a reproduction frequency band of each speaker unit are generally provided. In recent years, the following speaker systems where a network circuit corresponding to a woofer and a network circuit corresponding to a tweeter can be independent from each other are widely used (hereinafter, abbreviated as a biwiring SS). Such systems have input terminals connected to these network circuits, respectively, and are compatible with biwiring connection. The biwiring connection adopts biamplifying drive using a power amplifier to be connected to the network circuit of the woofer and another power amplifier to be connected to the network circuit of the tweeter.
On the other hand, in a method for realizing the multi amplifying (bi-amplifying) drive without using the network circuits of the speaker system, a channel divider is provided in a previous stage of the power amplifier, and the channel divider occasionally divides a band of a sound signal. The channel divider divides a band of an input sound signal into at least a low-pitched output signal and a high-pitched output signal so as to output the signals to a multi-amplifier in a sound reproducing system of the above multi-amplifier and multiway speaker system. The use of the channel divider provides advantages such that an LPF (low-pass filter) having an excess band steeper than that of the network of a speaker system or an HPF (high-pass filter) can be set, and a crossover frequency can be set comparatively freely (for example, Japanese Patent Application Laid-Open No. 2005-109969). When the channel divider is adopted, since a low-pitched amplifying circuit and a high-pitched amplifying circuit are independent from each other, cross-modulation distortion generated due to superimposing of a low frequency component and a high frequency component is reduced, and thus reproduction sound quality is excellent.
In recent years, some DSPs are provided with a function of the channel divider so that a speaker system without a network circuit can be connected by using an AV receiver including the DSP and a multi-amplifier (Japanese Patent Application Laid-Open Nos. 2002-111399 and 2005-184149). When the channel divider is realized by a digital filter, an FIR filter or an IIR filter is occasionally used. In order to use the channel divider, a reproduction band of each speaker unit in the speaker system should be measured by using a microphone, and a crossover frequency should be suitably set (Japanese Patent No. 4321315, and Japanese Utility Model Application Laid-Open No. 5-39097 (1993)).
In conventional channel divider, when a crossover frequency is set between a woofer and a tweeter, this is automatically applied to a cutoff frequency between a low-pitched LPF and a high-pitched HPF. Certainly, a channel divider where a cutoff frequency of a low-pitched LPF and a cutoff frequency of a high-pitched HPF can be set independently is surely present. Since reproducible range of a woofer and a reproducible range of a tweeter are mostly overlapped with each other under use condition without using a network circuit, cutoff frequencies of filters in charge of adjacent frequency bands are mostly set to uniform values in the overlapped bands.
However, even when the channel divider is tried to be used in the sound reproducing system, it is very difficult for general users except for some users to structure a speaker system without a network circuit (a marketed production is converted, the speaker system is built by using only units or the like) and to set a suitable crossover frequency using a microphone. Even when a biamp drive is enabled by using a multichannel amplifying circuit, a domestic audio device such as an AV receiver rarely adopts the function of the channel divider.
On the other hand, when the biamp drive is tried to be realized by using biwiring SS including a common network circuit and a channel divider, it is actually difficult to set a crossover frequency. Since the biwiring SS including a network circuit is designed so as to obtain a predetermined flat synthesized characteristic, when the channel divider sets a crossover frequency at a previous stage of the multichannel amplifying circuit to divide a band, as a result, dip is occasionally generated in a sound pressure frequency characteristic. When crossover frequency set by the channel divider is shifted from the crossover frequency of the biwiring SS, the dip on the sound pressure frequency characteristic increases, and thus a band where suitable reproduction is not carried out is widened. Further, when a measuring device such as the microphone, a level meter or an FFT analyzer is not provided, it is difficult for general users to understand an unknown crossover frequency of the biwiring SS, and thus it is occasionally difficult for general users to set the crossover frequency through the channel divider.